1. Field of the Invention
The present invention generally relates to solar cells and methods and apparatuses for forming the same. More particularly, the present invention relates to thin film solar cells and methods and apparatuses for forming the same including steps used to control contamination and improve device yield.
2. Description of the Related Art
Plasma enhanced chemical vapor deposition (PECVD) chambers for the deposition of semiconductor materials on substrates is well known in the art. Examples of such PECVD chambers are shown in U.S. Pat. No. 6,477,980 and published Patent Application US 20060060138 each of which is incorporated herein by this reference. Plasma processes include supplying a process gas mixture to a vacuum chamber called a plasma chamber and then applying electromagnetic energy to excite the process gas to a plasma state. The plasma decomposes the gas mixture into ion species that perform the desired deposition on an appropriate substrate.
The silicon solar cells formed by such deposition processes on an appropriate substrate include layers of amorphous silicon as well as micro-crystalline silicon. These layers form the p-i-n devices which absorb solar radiation and as a result, generate electrical current. In performing the desired deposition to form the p-i-n structures it is important that contamination of the i-layers does not occur during the i-layer formation process from prior deposited p-type and n-type deposited layers that may be formed in the same or subsequent processing chambers in a processing sequence. In the prior art, separate deposition chambers are commonly used to form each of the desired layers of a device. Such a process is quite slow and requires an inordinate amount of time to complete thus creating high production costs for solar cells formed by these techniques. To overcome this problem a multiple PECVD chamber apparatus has been developed which allows substrates including large substrates, to be automatically handled and transferred between the PECVD chambers to accomplish the desired deposition. Even when such deposition occurs, the throughput can be inadequate to obtain the desired production efficiencies and the achieved contamination levels can lead to a low device yield and generally poor device performance characteristics.
It is therefore desirous of having a solar cell production apparatus which includes a plurality of PECVD chambers to improve the overall throughput of the system, and improve the contamination levels in the produced cell to improve the formed device's electrical performance and the processing sequence's device yield.